(1) Field of the Invention
The present invention relates to communication system using an electric power line and particularly relates to data collecting technology on electric household appliances in electric power line communication system at home.
(2) Description of the Prior Art
Conventionally, technology of collecting data from appliances using an electric power line in home network is disclosed in the Japanese Laid-Open Patent Application Nos. H7-312649 and H10-271572. The technology of the Japanese Laid-Open Patent Application No. H7-312649 is a system in which a power transmission communication device collects sampling data held in plural terminals through an electric power line. The technology of the Japanese Laid-Open Patent No. H10-271572 is a system in which an information collecting device collects meter-reading information of a power meter placed in each household and information of a home-care support system, a household security service support system and a home automation system through an electric power line.
In the above-mentioned structures, however, it is a premise that the data collecting device is connected to the electric power line at all times but a portable display terminal that collects data on appliances may not be connected to the electric power line. In this case, the display terminal cannot collect data while it is not connected to the electric power line, and therefore there is a drawback that the display terminal cannot display the correct data on the screen even though it tries to refer to the past data because the data are not acquired. Additionally, in the system that the storage capacity of the display terminal is not enough to hold the large quantity of data on the appliances and therefore the display terminal must acquire the data from a controller every time it displays the data. Further, when the display terminal analyzes and displays the data frequently or the data quantity is large, there is also a problem that the communication quantity becomes enormous, communication efficiency deteriorates and furthermore the display response is degraded.